Cheksum has been fixed so the game runs fine on a US/EUR console (if someone ever wants to make a cartmod).

Technical part:

Horizontal speed for player 1 is stored in RAM @ $C018
Vertical speed for player 1 is stored in RAM @ $C019
Horizontal speed for player 2 is stored in RAM @ $C01A
Vertical speed for player 2 is stored in RAM @ $C01B